# .NET SDK Reference Copy page [![Star on GitHub](https://img.shields.io/github/stars/configcat/.net-sdk.svg?style=social)](https://github.com/configcat/.net-sdk/stargazers) [![Build status](https://github.com/configcat/.net-sdk/actions/workflows/dotnet-sdk-ci.yml/badge.svg?branch=master)](https://github.com/configcat/.net-sdk/actions/workflows/dotnet-sdk-ci.yml) [![NuGet Version](https://img.shields.io/nuget/v/ConfigCat.Client)](https://www.nuget.org/packages/ConfigCat.Client/) [![Sonar Coverage](https://img.shields.io/sonar/coverage/net-sdk?logo=SonarCloud\&server=https%3A%2F%2Fsonarcloud.io)](https://sonarcloud.io/project/overview?id=net-sdk) [![Quality Gate Status](https://sonarcloud.io/api/project_badges/measure?project=net-sdk\&metric=alert_status)](https://sonarcloud.io/dashboard?id=net-sdk) [ConfigCat .NET SDK on GitHub](https://github.com/configcat/.net-sdk) ## Getting started[​](#getting-started "Direct link to Getting started") ### 1. Install *ConfigCat SDK* [NuGet package](https://www.nuget.org/packages/ConfigCat.Client)[​](#1-install-configcat-sdk-nuget-package "Direct link to 1-install-configcat-sdk-nuget-package") * Powershell / NuGet Package Manager Console * .NET CLI ```powershell Install-Package ConfigCat.Client ``` ```text dotnet add package ConfigCat.Client ``` info To get the *ConfigCat SDK* up and running in Unity, please refer to [this guide](https://configcat.com/docs/sdk-reference/unity.md). ### 2. Import package[​](#2-import-package "Direct link to 2. Import package") ```csharp using ConfigCat.Client; ``` ### 3. Create the *ConfigCat* client with your *SDK Key*[​](#3-create-the-configcat-client-with-your-sdk-key "Direct link to 3-create-the-configcat-client-with-your-sdk-key") ```csharp var client = ConfigCatClient.Get("#YOUR-SDK-KEY#"); ``` ### 4. Get your setting value[​](#4-get-your-setting-value "Direct link to 4. Get your setting value") ```csharp var isMyAwesomeFeatureEnabled = await client.GetValueAsync("isMyAwesomeFeatureEnabled", false); if (isMyAwesomeFeatureEnabled) { doTheNewThing(); } else { doTheOldThing(); } ``` The *ConfigCat SDK* also offers a synchronous API for feature flag evaluation. Read more [here](#snapshots-and-non-blocking-synchronous-feature-flag-evaluation). ### 5. Dispose the *ConfigCat* client[​](#5-dispose-the-configcat-client "Direct link to 5-dispose-the-configcat-client") You can safely dispose all clients at once or individually and release all associated resources on application exit. ```csharp ConfigCatClient.DisposeAll(); // disposes all clients // -or- client.Dispose(); // disposes a specific client ``` ## Creating the *ConfigCat Client*[​](#creating-the-configcat-client "Direct link to creating-the-configcat-client") *ConfigCat Client* is responsible for: * managing the communication between your application and ConfigCat servers. * caching your setting values and feature flags. * serving values quickly in a failsafe way. `ConfigCatClient.Get(sdkKey: "")` returns a client with default options. ### Customizing the *ConfigCat Client*[​](#customizing-the-configcat-client "Direct link to customizing-the-configcat-client") To customize the SDK's behavior, you can pass an additional `Action` parameter to the `Get()` static factory method where the `ConfigCatClientOptions` class is used to set up the *ConfigCat Client*. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.ManualPoll; options.Logger = new ConsoleLogger(LogLevel.Info); }); ``` These are the available options on the `ConfigCatClientOptions` class: | Properties | Description | Default | | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------- | | `PollingMode` | Optional, sets the polling mode for the client. [More about polling modes](#polling-modes). | `PollingModes.AutoPoll()` | | `ConfigFetcher` | Optional, [`IConfigCatConfigFetcher`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/ConfigService/IConfigCatConfigFetcher.cs) instance for downloading a config. | [`HttpClientConfigFetcher`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/ConfigService/HttpClientConfigFetcher.cs) | | `ConfigCache` | Optional, [`IConfigCatCache`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/Cache/IConfigCatCache.cs) instance for caching the downloaded config. | [`InMemoryConfigCache`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/Cache/InMemoryConfigCache.cs) | | `Logger` | Optional, [`IConfigCatLogger`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/Logging/IConfigCatLogger.cs) instance for tracing. | [`ConsoleLogger`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/Logging/ConsoleLogger.cs) (with WARNING level) | | `LogFilter` | Optional, sets a custom log filter. [More about log filtering](#log-filtering). | `null` (none) | | `BaseUrl` | Optional, sets the CDN base url (forward proxy, dedicated subscription) from where the SDK will download the config JSON. | | | `Proxy` | Optional, [`IWebProxy`](https://learn.microsoft.com/en-us/dotnet/api/system.net.iwebproxy) instance that provides settings for routing HTTP requests made by the SDK through an HTTP, HTTPS, SOCKS, etc. proxy. [More about the proxy settings](#using-configcat-behind-a-proxy). | | | `HttpTimeout` | Optional, sets the underlying HTTP client's timeout. [More about the HTTP timeout](#http-timeout). | `TimeSpan.FromSeconds(30)` | | `FlagOverrides` | Optional, sets the local feature flag & setting overrides. [More about feature flag overrides](#flag-overrides). | | | `DataGovernance` | Optional, describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. [More about Data Governance](https://configcat.com/docs/advanced/data-governance.md). Available options: `Global`, `EuOnly` | `Global` | | `DefaultUser` | Optional, sets the default user. [More about default user](#default-user). | `null` (none) | | `Offline` | Optional, determines whether the client should be initialized to offline mode. [More about offline mode](#online--offline-mode). | `false` | Via the events provided by `ConfigCatClientOptions` you can also subscribe to the hooks (events) at the time of initialization. [More about hooks](#hooks). For example: ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.ClientReady += (s, e) => { var keys = ((IConfigCatClient)s).Snapshot().GetAllKeys(); Console.WriteLine("Client is ready! Number of available feature flags: " + keys.Count); }; }); ``` info You can acquire singleton client instances for your SDK keys using the `ConfigCatClient.Get(sdkKey: "")` static factory method. (However, please keep in mind that subsequent calls to `ConfigCatClient.Get()` with the *same SDK Key* return a *shared* client instance, which was set up by the first call.) You can close all open clients at once using the `ConfigCatClient.DisposeAll()` method or do it individually using the `client.Dispose()` method. ## Anatomy of `GetValueAsync()`[​](#anatomy-of-getvalueasync "Direct link to anatomy-of-getvalueasync") | Parameters | Description | | -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- | | `key` | **REQUIRED.** The key of a specific setting or feature flag. Set on *ConfigCat Dashboard* for each setting. | | `defaultValue` | **REQUIRED.** This value will be returned in case of an error. | | `user` | Optional, *User Object*. Essential when using Targeting. [Read more about Targeting.](https://configcat.com/docs/targeting/targeting-overview.md) | ```csharp User userObject = new User("#UNIQUE-USER-IDENTIFIER#"); // Optional User Object var value = await client.GetValueAsync("keyOfMyFeatureFlag", false, userObject); ``` caution It is important to provide an argument for the `defaultValue` parameter, specifically for the `T` generic type parameter, that matches the type of the feature flag or setting you are evaluating. Please refer to the following table for the corresponding types. ### Setting type mapping[​](#setting-type-mapping "Direct link to Setting type mapping") | Setting Kind | Type parameter `T` | | -------------- | --------------------------------- | | On/Off Toggle | `bool` / `bool?` | | Text | `string` / `string?` | | Whole Number | `int` / `int?` / `long` / `long?` | | Decimal Number | `double` / `double?` | In addition to the types mentioned above, you also have the option to provide `object` or `object?` for the type parameter regardless of the setting kind. However, this approach is not recommended as it may involve [boxing](https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/types/boxing-and-unboxing). It's important to note that providing any other type for the type parameter will result in an `ArgumentException`. If you specify an allowed type but it mismatches the setting kind, an error message will be logged and `defaultValue` will be returned. When relying on type inference and not explicitly specifying the type parameter, be mindful of potential type mismatch issues, especially with number types. For example, `client.GetValueAsync("keyOfMyDecimalSetting", 0)` will return `defaultValue` (`0`) instead of the actual value of the decimal setting because the compiler infers the type as `int` instead of `double`, that is, the call is equivalent to `client.GetValueAsync("keyOfMyDecimalSetting", 0)`, which is a type mismatch. To correctly evaluate a decimal setting, you should use: ```csharp var value = await client.GetValueAsync("keyOfMyDecimalSetting", 0.0); // -or- var value = await client.GetValueAsync("keyOfMyDecimalSetting", 0d); // -or- var value = await client.GetValueAsync("keyOfMyDecimalSetting", 0); ``` ## Anatomy of `GetValueDetailsAsync()`[​](#anatomy-of-getvaluedetailsasync "Direct link to anatomy-of-getvaluedetailsasync") `GetValueDetailsAsync()` is similar to `GetValueAsync()` but instead of returning the evaluated value only, it provides more detailed information about the evaluation result. | Parameters | Description | | -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- | | `key` | **REQUIRED.** The key of a specific setting or feature flag. Set on *ConfigCat Dashboard* for each setting. | | `defaultValue` | **REQUIRED.** This value will be returned in case of an error. | | `user` | Optional, *User Object*. Essential when using Targeting. [Read more about Targeting.](https://configcat.com/docs/targeting/targeting-overview.md) | ```csharp User userObject = new User("#UNIQUE-USER-IDENTIFIER#"); // Optional User Object var details = await client.GetValueDetailsAsync("keyOfMyFeatureFlag", false, userObject); ``` caution It is important to provide an argument for the `defaultValue` parameter, specifically for the `T` generic type parameter, that matches the type of the feature flag or setting you are evaluating. Please refer to [this table](#setting-type-mapping) for the corresponding types. The `details` result contains the following information: | Field | Type | Description | | ------------------------- | ------------------------------------ | ---------------------------------------------------------------------------------------------------------- | | `Key` | `string` | The key of the evaluated feature flag or setting. | | `Value` | `bool` / `string` / `int` / `double` | The evaluated value of the feature flag or setting. | | `User` | `User` | The User Object used for the evaluation. | | `IsDefaultValue` | `bool` | True when the default value passed to `GetValueDetailsAsync()` is returned due to an error. | | `ErrorCode` | `EvaluationErrorCode` | In case of an error, this property contains a code that identifies the reason for the error. | | `ErrorMessage` | `string` | In case of an error, this property contains the error message. | | `ErrorException` | `Exception` | In case of an error, this property contains the related exception object (if any). | | `MatchedTargetingRule` | `ITargetingRule` | The Targeting Rule (if any) that matched during the evaluation and was used to return the evaluated value. | | `MatchedPercentageOption` | `IPercentageOption` | The Percentage Option (if any) that was used to select the evaluated value. | | `FetchTime` | `DateTime` | The last download time (UTC) of the current config. | ## User Object[​](#user-object "Direct link to User Object") The [User Object](https://configcat.com/docs/targeting/user-object.md) is essential if you'd like to use ConfigCat's [Targeting](https://configcat.com/docs/targeting/targeting-overview.md) feature. ```csharp User userObject = new User("#UNIQUE-USER-IDENTIFIER#"); ``` ```csharp User userObject = new User("john@example.com"); ``` | Parameters | Description | | ---------- | ------------------------------------------------------------------------------------------------------------------------------- | | `Id` | **REQUIRED.** Unique identifier of a user in your application. Can be any `string` value, even an email address. | | `Email` | Optional parameter for easier Targeting Rule definitions. | | `Country` | Optional parameter for easier Targeting Rule definitions. | | `Custom` | Optional dictionary for custom attributes of a user for advanced Targeting Rule definitions. E.g. User role, Subscription type. | ```csharp User userObject = new User("#UNIQUE-USER-IDENTIFIER#") { Email = "john@example.com", Country = "United Kingdom", Custom = { ["SubscriptionType"] = "Pro", ["UserRole"] = "Admin" } }; ``` The `Custom` dictionary also allows attribute values other than `string` values: ```csharp User userObject = new User("#UNIQUE-USER-IDENTIFIER#") { Custom = { ["Rating"] = 4.5, ["RegisteredAt"] = DateTimeOffset.Parse("2023-11-22 12:34:56 +00:00", CultureInfo.InvariantCulture), ["Roles"] = new[] { "Role1", "Role2" } } }; ``` ### User Object Attribute Types[​](#user-object-attribute-types "Direct link to User Object Attribute Types") All comparators support `string` values as User Object attribute (in some cases they need to be provided in a specific format though, see below), but some of them also support other types of values. It depends on the comparator how the values will be handled. The following rules apply: **Text-based comparators** (EQUALS, IS ONE OF, etc.) * accept `string` values, * all other values are automatically converted to `string` (a warning will be logged but evaluation will continue as normal). **SemVer-based comparators** (IS ONE OF, <, >=, etc.) * accept `string` values containing a properly formatted, valid semver value, * all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped). **Number-based comparators** (=, <, >=, etc.) * accept `double` values and all other numeric values which can safely be converted to `double`, * accept `string` values containing a properly formatted, valid `double` value, * all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped). **Date time-based comparators** (BEFORE / AFTER) * accept `DateTime` or `DateTimeOffset` values, which are automatically converted to a second-based Unix timestamp, * accept `double` values representing a second-based Unix timestamp and all other numeric values which can safely be converted to `double`, * accept `string` values containing a properly formatted, valid `double` value, * all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped). **String array-based comparators** (ARRAY CONTAINS ANY OF / ARRAY NOT CONTAINS ANY OF) * accept arrays of `string`, * accept `string` values containing a valid JSON string which can be deserialized to an array of `string`, * all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped). ### Default user[​](#default-user "Direct link to Default user") It's possible to set a default User Object that will be used on feature flag and setting evaluation. It can be useful when your application has a single user only or rarely switches users. You can set the default User Object either on SDK initialization: ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => options.DefaultUser = new User(identifier: "john@example.com")); ``` ...or using the `SetDefaultUser()` method of the `ConfigCatClient` object: ```csharp client.SetDefaultUser(new User(identifier: "john@example.com")); ``` Whenever the evaluation methods like `GetValueAsync()`, `GetValueDetailsAsync()`, etc. are called without an explicit `user` parameter, the SDK will automatically use the default user as a User Object. ```csharp var user = new User(identifier: "john@example.com"); client.SetDefaultUser(user); // The default user will be used in the evaluation process. var value = await client.GetValueAsync(key: "keyOfMyFeatureFlag", defaultValue: false); ``` When a `user` parameter is passed to the evaluation methods, it takes precedence over the default user. ```csharp var user = new User(identifier: "john@example.com"); client.SetDefaultUser(user); var otherUser = new User(identifier: "brian@example.com"); // otherUser will be used in the evaluation process. var value = await client.GetValueAsync(key: "keyOfMyFeatureFlag", defaultValue: false, user: otherUser); ``` You can also remove the default user by doing the following: ```csharp client.ClearDefaultUser(); ``` ## Polling Modes[​](#polling-modes "Direct link to Polling Modes") The *ConfigCat SDK* supports 3 different polling strategies to fetch feature flags and settings from the ConfigCat CDN. Once the latest data is downloaded, it is stored in the cache, then calls to `GetValueAsync()` use the cached data to evaluate feature flags and settings. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle. [More about polling modes.](https://configcat.com/docs/advanced/caching.md) ### Auto polling (default)[​](#auto-polling-default "Direct link to Auto polling (default)") The *ConfigCat SDK* downloads the latest config data from the ConfigCat CDN automatically every 60 seconds and stores it in the cache. Use the `pollInterval` option parameter to change the polling interval. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.AutoPoll(pollInterval: TimeSpan.FromSeconds(95)); }); ``` Available options: | Option Parameter | Description | Default | | ----------------- | ---------------------------------------------------------------------------------------- | ------- | | `pollInterval` | Polling interval. | 60s | | `maxInitWaitTime` | Maximum waiting time between the client initialization and the first config acquisition. | 5s | ### Lazy loading[​](#lazy-loading "Direct link to Lazy loading") When calling `GetValueAsync()`, the *ConfigCat SDK* downloads the latest config data from the ConfigCat CDN only if it is not already present in the cache, or if the cache has expired. In this case `GetValueAsync()` will return the setting value after the cache is updated. Use `cacheTimeToLive` parameter to manage configuration lifetime. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.LazyLoad(cacheTimeToLive: TimeSpan.FromSeconds(600)); }); ``` Available options: | Option Parameter | Description | Default | | ----------------- | ----------- | ------- | | `cacheTimeToLive` | Cache TTL. | 60s | ### Manual polling[​](#manual-polling "Direct link to Manual polling") Manual polling gives you full control over when the config data is downloaded from the ConfigCat CDN. The *ConfigCat SDK* will not download it automatically. Calling `ForceRefreshAsync()` is your application's responsibility. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.ManualPoll; }); await client.ForceRefreshAsync(); ``` > `GetValueAsync()` returns `defaultValue` if the cache is empty. Call `ForceRefreshAsync()` to update the cache. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.ManualPoll; }); Console.WriteLine(await client.GetValueAsync("keyOfMyTextSetting", "my default value")); // console: "my default value" await client.ForceRefreshAsync(); Console.WriteLine(await client.GetValueAsync("keyOfMyTextSetting", "my default value")); // console: "value from server" ``` ## Hooks[​](#hooks "Direct link to Hooks") The SDK provides several hooks (events), by means of which you can get notified of its actions. Via the following events you can subscribe to particular events raised by the *ConfigCat* client: * `event EventHandler ClientReady`: This event is raised when the client reaches the ready state, i.e. completes initialization. * If Lazy Loading or Manual Polling is used, it's considered ready right after the initial sync with the external cache (if any) completes. * If Auto Polling is used, the ready state is reached as soon as * the initial sync with the external cache yields up-to-date config data, * otherwise, if the client is online (i.e. HTTP requests are allowed), the first config fetch operation completes (regardless of success or failure), * or the time specified via Auto Polling's `maxInitWaitTime` option has passed. Reaching the ready state usually means the client is ready to evaluate feature flags and settings. However, please note that this is not guaranteed. In case of initialization failure or timeout, the internal cache may be empty or expired even after the ready state is reported. You can verify this by checking the `CacheState` property of the event arguments. * `event EventHandler ConfigFetched`: This event is raised each time the client attempts to refresh the cached config by fetching the latest version from the ConfigCat CDN. It is raised not only when `ForceRefreshAsync` is called but also when the refresh is initiated by the client automatically. Thus, this event allows you to observe potential network issues that occur under the hood. * `event EventHandler ConfigChanged`: This event is raised first when the client's internal cache gets populated. Afterwards, it is raised again each time the internally cached config is updated to a newer version, either as a result of synchronization with the external cache, or as a result of fetching a newer version from the ConfigCat CDN. * `event EventHandler FlagEvaluated`: This event is raised each time the client evaluates a feature flag or setting. The event provides the same evaluation details that you would get from [`GetValueDetailsAsync()`](#anatomy-of-getvaluedetailsasync). * `event EventHandler Error`: This event is raised when an error occurs within the client. You can subscribe to these events either on initialization: ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.PollingMode = PollingModes.ManualPoll; options.FlagEvaluated += (s, e) => { /* handle the event */ }; }); ``` ...or directly on the `ConfigCatClient` instance: ```csharp client.FlagEvaluated += (s, e) => { /* handle the event */ }; ``` caution Some events (e.g. `ClientReady`, `ConfigChanged` and `Error`) may be raised before `ConfigCatClient.Get` returns. This means you may miss them unless you subscribe on initialization. However, even if you do, there's another gotcha: it's not safe to use the outer `client` variable in your event handler because it may not yet be assigned when the handler is called. Instead, you can safely access the client instance via the sender parameter like `var client = (IConfigCatClient)s;`. ## Snapshots and non-blocking synchronous feature flag evaluation[​](#snapshots-and-non-blocking-synchronous-feature-flag-evaluation "Direct link to Snapshots and non-blocking synchronous feature flag evaluation") Currently, the *ConfigCat* client provides both asynchronous and synchronous methods for evaluating feature flags and settings. However, depending on the setup, the synchronous methods may block the executing thread for longer periods of time (e.g. when downloading config data from the ConfigCat CDN servers), which can lead to an unresponsive application. To prevent such issues, the problematic methods have been deprecated and are going to be removed in a future major version. As an alternative, since v9.2.0, the .NET SDK provides a way to synchronously evaluate feature flags and settings as a non-blocking operation, via *snapshots*. Using the `Snapshot()` method, you can capture the current state of the *ConfigCat* client (including the latest downloaded config data) and use the resulting snapshot object to synchronously evaluate feature flags and settings based on the captured state: ```csharp using var client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => options.PollingMode = PollingModes.AutoPoll()); // Wait for the client to initialize. await client.WaitForReadyAsync(); var snapshot = client.Snapshot(); var user = new User("#UNIQUE-USER-IDENTIFIER#"); foreach (var key in snapshot.GetAllKeys()) { var value = snapshot.GetValue(key, default(object), user); Console.WriteLine($"{key}: {value}"); } ``` Creating a snapshot is a cheap operation. This is possible because snapshots capture the client's internal (in-memory) cache. No attempt is made to refresh the internal cache, even if it's empty or expired. caution Please note that creating and using a snapshot * won't trigger a sync with the external cache when working with [shared caching](https://configcat.com/docs/advanced/caching.md#shared-cache), * won't fetch the latest config data from the ConfigCat CDN when the internally cached config data is empty or expired. For the above reasons, it's recommended to use snapshots in conjunction with the Auto Polling mode, where the SDK automatically updates the internal cache in the background. (For other polling modes, you'll need to manually initiate a cache refresh by calling `ForceRefreshAsync`.) Because of this behavior, it's important to make sure that the client has completed initialization and populated its internal cache before creating snapshots. Otherwise the snapshot's evaluation methods won't have the data to do actual evaluation, but will just return the default value you pass to them. Which behavior is usually not what you want in your application. In Auto Polling mode, you can use the `WaitForReadyAsync` method to wait for the latest config data to become available locally. This is an asynchronous operation, which completes as soon as the client reaches the ready state, i.e. completes initialization (or the time specified via the `maxInitWaitTime` option passes). (Please note that this doesn't apply to other polling modes. In those cases, the client doesn't contact the ConfigCat CDN during initialization, so the ready state is reached as soon as the first sync with the external cache completes.) Typically, you call `WaitForReadyAsync` and wait for its completion only once, in the initialization phase of your application. caution Reaching the ready state usually means the client is ready to evaluate feature flags and settings. However, please note that this is not guaranteed. In case of initialization failure or timeout, the internal cache may be empty or expired even after the ready state is reported. You can verify this by checking the return value. ```csharp var clientCacheState = await client.WaitForReadyAsync(); if (clientCacheState == ClientCacheState.NoFlagData) { // Handle initialization failure (see below). Console.WriteLine("ConfigCat client failed to obtain the config data during initialization."); } ``` You have the following options to handle unsuccessful initialization: * If it's acceptable for your application to start up and use the default values passed to the evaluation methods, you may log some warning (or skip the check altogether as the client will log warnings anyway), and let the application continue. * Otherwise, you need to either terminate the application or continue waiting. The latter is an option because the client might be able to obtain the config data later, in the case of a transient problem like some temporary network issue. However, the *ConfigCat SDK* doesn't provide out-of-the-box support for this case currently. You can implement this logic by subscribing to the `ConfigChanged` hook and waiting for the first event. ## Online / Offline mode[​](#online--offline-mode "Direct link to Online / Offline mode") In cases where you want to prevent the SDK from making HTTP calls, you can switch it to offline mode: ```csharp client.SetOffline(); ``` In offline mode, the SDK won't initiate HTTP requests and will work only from its cache. To switch the SDK back to online mode, do the following: ```csharp client.SetOnline(); ``` Using the `client.IsOffline` property you can check whether the SDK is in offline mode. ## Flag Overrides[​](#flag-overrides "Direct link to Flag Overrides") With flag overrides you can overwrite the feature flags & settings downloaded from the ConfigCat CDN with local values. Moreover, you can specify how the overrides should apply over the downloaded values. The following 3 behaviours are supported: * **Local only** (`OverrideBehaviour.LocalOnly`): When evaluating values, the SDK will not use feature flags & settings from the ConfigCat CDN, but it will use all feature flags & settings that are loaded from local-override sources. * **Local over remote** (`OverrideBehaviour.LocalOverRemote`): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the local-override version will take precedence. * **Remote over local** (`OverrideBehaviour.RemoteOverLocal`): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the downloaded version will take precedence. You can load your feature flag & setting overrides from a file or from a simple `Dictionary` structure. ### JSON File[​](#json-file "Direct link to JSON File") The SDK can load your feature flag & setting overrides from a file. You can also specify whether the file should be reloaded when it gets modified. #### File[​](#file "Direct link to File") ```csharp IConfigCatClient client = ConfigCatClient.Get("localhost", options => { options.FlagOverrides = FlagOverrides.LocalFile( "path/to/local_flags.json", // path to the file true, // reload the file when it gets modified OverrideBehaviour.LocalOnly ); }); ``` #### JSON File Structure[​](#json-file-structure "Direct link to JSON File Structure") The SDK supports 2 types of JSON structures to describe feature flags & settings. ##### 1. Simple (key-value) structure[​](#1-simple-key-value-structure "Direct link to 1. Simple (key-value) structure") ```json { "flags": { "enabledFeature": true, "disabledFeature": false, "intSetting": 5, "doubleSetting": 3.14, "stringSetting": "test" } } ``` ##### 2. Complex (full-featured) structure[​](#2-complex-full-featured-structure "Direct link to 2. Complex (full-featured) structure") This is the same format that the SDK downloads from the ConfigCat CDN. It allows the usage of all features that are available on the ConfigCat Dashboard. You can download your current config JSON from ConfigCat's CDN and use it as a baseline. A convenient way to get the config JSON for a specific SDK Key is to install the [ConfigCat CLI](https://github.com/configcat/cli) tool and execute the following command: ```bash configcat config-json get -f v6 -p {YOUR-SDK-KEY} > config.json ``` (Depending on your [Data Governance](https://configcat.com/docs/advanced/data-governance.md) settings, you may need to add the `--eu` switch.) Alternatively, you can download the config JSON manually, based on your [Data Governance](https://configcat.com/docs/advanced/data-governance.md) settings: * GLOBAL: `https://cdn-global.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v6.json` * EU: `https://cdn-eu.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v6.json` ```json { "p": { // hash salt, required only when confidential text comparator(s) are used "s": "80xCU/SlDz1lCiWFaxIBjyJeJecWjq46T4eu6GtozkM=" }, "s": [ // array of segments { "n": "Beta Users", // segment name "r": [ // array of User Conditions (there is a logical AND relation between the elements) { "a": "Email", // comparison attribute "c": 0, // comparator (see below) "l": [ // comparison value (see below) "john@example.com", "jane@example.com" ] } ] } ], "f": { // key-value map of feature flags & settings "isFeatureEnabled": { // key of a particular flag / setting "t": 0, // setting type, possible values: // 0 -> on/off setting (feature flag) // 1 -> text setting // 2 -> whole number setting // 3 -> decimal number setting "r": [ // array of Targeting Rules (there is a logical OR relation between the elements) { "c": [ // array of conditions (there is a logical AND relation between the elements) { "u": { // User Condition "a": "Email", // comparison attribute "c": 2, // comparator, possible values and required comparison value types: // 0 -> IS ONE OF (cleartext) + string array comparison value ("l") // 1 -> IS NOT ONE OF (cleartext) + string array comparison value ("l") // 2 -> CONTAINS ANY OF (cleartext) + string array comparison value ("l") // 3 -> NOT CONTAINS ANY OF (cleartext) + string array comparison value ("l") // 4 -> IS ONE OF (semver) + semver string array comparison value ("l") // 5 -> IS NOT ONE OF (semver) + semver string array comparison value ("l") // 6 -> < (semver) + semver string comparison value ("s") // 7 -> <= (semver + semver string comparison value ("s") // 8 -> > (semver) + semver string comparison value ("s") // 9 -> >= (semver + semver string comparison value ("s") // 10 -> = (number) + number comparison value ("d") // 11 -> <> (number + number comparison value ("d") // 12 -> < (number) + number comparison value ("d") // 13 -> <= (number + number comparison value ("d") // 14 -> > (number) + number comparison value ("d") // 15 -> >= (number) + number comparison value ("d") // 16 -> IS ONE OF (hashed) + string array comparison value ("l") // 17 -> IS NOT ONE OF (hashed) + string array comparison value ("l") // 18 -> BEFORE (UTC datetime) + second-based Unix timestamp number comparison value ("d") // 19 -> AFTER (UTC datetime) + second-based Unix timestamp number comparison value ("d") // 20 -> EQUALS (hashed) + string comparison value ("s") // 21 -> NOT EQUALS (hashed) + string comparison value ("s") // 22 -> STARTS WITH ANY OF (hashed) + string array comparison value ("l") // 23 -> NOT STARTS WITH ANY OF (hashed) + string array comparison value ("l") // 24 -> ENDS WITH ANY OF (hashed) + string array comparison value ("l") // 25 -> NOT ENDS WITH ANY OF (hashed) + string array comparison value ("l") // 26 -> ARRAY CONTAINS ANY OF (hashed) + string array comparison value ("l") // 27 -> ARRAY NOT CONTAINS ANY OF (hashed) + string array comparison value ("l") // 28 -> EQUALS (cleartext) + string comparison value ("s") // 29 -> NOT EQUALS (cleartext) + string comparison value ("s") // 30 -> STARTS WITH ANY OF (cleartext) + string array comparison value ("l") // 31 -> NOT STARTS WITH ANY OF (cleartext) + string array comparison value ("l") // 32 -> ENDS WITH ANY OF (cleartext) + string array comparison value ("l") // 33 -> NOT ENDS WITH ANY OF (cleartext + string array comparison value ("l") // 34 -> ARRAY CONTAINS ANY OF (cleartext) + string array comparison value ("l") // 35 -> ARRAY NOT CONTAINS ANY OF (cleartext) + string array comparison value ("l") "l": [ // comparison value - depending on the comparator, another type of value may need // to be specified (see above): // "s": string // "d": number "@example.com" ] } }, { "p": { // Flag Condition (Prerequisite) "f": "mainIntFlag", // key of prerequisite flag "c": 0, // comparator, possible values: 0 -> EQUALS, 1 -> NOT EQUALS "v": { // comparison value (value's type must match the prerequisite flag's type) "i": 42 } } }, { "s": { // Segment Condition "s": 0, // segment index, a valid index into the top-level segment array ("s") "c": 1 // comparator, possible values: 0 -> IS IN SEGMENT, 1 -> IS NOT IN SEGMENT } } ], "s": { // alternatively, an array of Percentage Options ("p", see below) can also be specified "v": { // the value served when the rule is selected during evaluation "b": true }, "i": "bcfb84a7" } } ], "p": [ // array of Percentage Options { "p": 10, // % value "v": { // the value served when the Percentage Option is selected during evaluation "b": true }, "i": "bcfb84a7" }, { "p": 90, "v": { "b": false }, "i": "bddac6ae" } ], "v": { // fallback value, served when none of the Targeting Rules match, // no Percentage Options are defined or evaluation of these is not possible "b": false // depending on the setting type, another type of value may need to be specified: // text setting -> "s": string // whole number setting -> "i": number // decimal number setting -> "d": number }, "i": "430bded3" // variation id (for analytical purposes) } } } ``` For a more comprehensive specification of the config JSON v6 format, you may refer to [this JSON schema document](https://github.com/configcat/config-json/blob/main/V6/config.schema.json). ### Dictionary[​](#dictionary "Direct link to Dictionary") You can set up the SDK to load your feature flag & setting overrides from a `Dictionary`. ```csharp var dictionary = new Dictionary { {"enabledFeature", true}, {"disabledFeature", false}, {"intSetting", 5}, {"doubleSetting", 3.14}, {"stringSetting", "test"}, }; IConfigCatClient client = ConfigCatClient.Get("localhost", options => { options.FlagOverrides = FlagOverrides.LocalDictionary(dictionary, OverrideBehaviour.LocalOnly); }); ``` ## Logging[​](#logging "Direct link to Logging") ### Setting log level[​](#setting-log-level "Direct link to Setting log level") ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#"); client.LogLevel = LogLevel.Info; ``` Available log levels: | Level | Description | | ------- | ------------------------------------------------------- | | Off | Nothing is logged. | | Error | Only error level events are logged. | | Warning | Default. Errors and Warnings are logged. | | Info | Errors, Warnings and feature flag evaluation is logged. | | Debug | All of the above plus debug info is logged. | Info level logging helps to inspect the feature flag evaluation process: ```bash ConfigCat.INFO [5000] Evaluating 'isPOCFeatureEnabled' for User '{"Identifier":"","Email":"configcat@example.com","Country":"US","SubscriptionType":"Pro","Role":"Admin","version":"1.0.0"}' Evaluating targeting rules and applying the first match if any: - IF User.Email CONTAINS ANY OF ['@something.com'] THEN 'False' => no match - IF User.Email CONTAINS ANY OF ['@example.com'] THEN 'True' => MATCH, applying rule Returning 'True'. ``` ### Custom logger implementation[​](#custom-logger-implementation "Direct link to Custom logger implementation") By default, the SDK logs to [the console's standard output](https://learn.microsoft.com/en-us/dotnet/api/system.console.out) but it also allows you to inject any custom logger implementation via the `ConfigCatClientOptions.Logger` property. Sample code on how to create a basic file logger implementation for ConfigCat client: [See Sample Code](https://github.com/configcat/.net-sdk/blob/master/samples/FileLoggerSample.cs) Another sample which shows how to implement an adapter to [the built-in logging framework](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/logging) of .NET Core/.NET 5+: [See Sample Code](https://github.com/configcat/.net-sdk/blob/master/samples/ASP.NETCore/WebApplication/Adapters/ConfigCatToMSLoggerAdapter.cs) ### Log Filtering[​](#log-filtering "Direct link to Log Filtering") You can define a custom log filter by providing a callback function via the `ConfigCatClientOptions.LogFilter` property. The callback will be called by the *ConfigCat SDK* each time a log event occurs (and the event passes the minimum log level specified by the `IConfigCatLogger.LogLevel` property). That is, the callback allows you to filter log events by `level`, `eventId`, `message` or `exception`. The formatted message string can be obtained via `message.InvariantFormattedMessage`. If the callback function returns `true`, the event will be logged, otherwise it will be skipped. ```cs // Filter out events with id 1001 from the log. LogFilterCallback logFilter = (LogLevel level, LogEventId eventId, ref FormattableLogMessage message, Exception? exception) => eventId != 1001; var client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => options.LogFilter = logFilter); ``` caution Please make sure that your log filter logic doesn't perform heavy computation and doesn't block the executing thread. A complex or incorrectly implemented log filter can degrade the performance of the SDK. ## `GetAllKeysAsync()`[​](#getallkeysasync "Direct link to getallkeysasync") You can get the keys for all available feature flags and settings by calling the `GetAllKeysAsync()` method of the `ConfigCatClient`. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#"); IEnumerable keys = await client.GetAllKeysAsync(); ``` ## `GetAllValuesAsync()`[​](#getallvaluesasync "Direct link to getallvaluesasync") Evaluates and returns the values of all feature flags and settings. Passing a [User Object](#user-object) is optional. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#"); IDictionary settingValues = await client.GetAllValuesAsync(); // invoke with User Object User userObject = new User("#UNIQUE-USER-IDENTIFIER#"); IDictionary settingValuesTargeting = await client.GetAllValuesAsync(userObject); ``` ## `GetAllValueDetailsAsync()`[​](#getallvaluedetailsasync "Direct link to getallvaluedetailsasync") Evaluates and returns the values along with evaluation details of all feature flags and settings. Passing a [User Object](#user-object) is optional. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#"); IReadOnlyList settingValues = await client.GetAllValueDetailsAsync(); // invoke with User Object User userObject = new User("435170f4-8a8b-4b67-a723-505ac7cdea92"); IReadOnlyList settingValuesTargeting = await client.GetAllValueDetailsAsync(userObject); ``` ## Using custom cache implementation[​](#using-custom-cache-implementation "Direct link to Using custom cache implementation") The *ConfigCat SDK* stores the downloaded config data in a local cache to minimize network traffic and enhance client performance. If you prefer to use your own cache solution, such as an external or distributed cache in your system, you can implement the [`IConfigCatCache`](https://github.com/configcat/.net-sdk/blob/master/src/ConfigCatClient/Cache/IConfigCatCache.cs) interface and set the `ConfigCache` parameter in the setup callback of `ConfigCatClient.Get`. This allows you to seamlessly integrate ConfigCat with your existing caching infrastructure. ```csharp public class MyCustomCache : IConfigCatCache { public string? Get(string key) { /* insert your synchronous cache read logic here */ } public Task GetAsync(string key, CancellationToken cancellationToken = default) { /* insert your asynchronous cache read logic here */ } public void Set(string key, string value) { /* insert your synchronous cache write logic here */ } public Task SetAsync(string key, string value, CancellationToken cancellationToken = default) { /* insert your asynchronous cache write logic here */ } } ``` then ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.ConfigCache = new MyCustomCache() }); ``` info The .NET SDK supports *shared caching*. You can read more about this feature and the required minimum SDK versions [here](https://configcat.com/docs/advanced/caching.md#shared-cache). ## Using ConfigCat behind a proxy[​](#using-configcat-behind-a-proxy "Direct link to Using ConfigCat behind a proxy") Provide your own network credentials (username/password) and proxy server settings (proxy server/port) by setting the `Proxy` property in the setup callback of `ConfigCatClient.Get`. ```csharp var myProxySettings = new WebProxy(proxyHost, proxyPort) { UseDefaultCredentials = false, Credentials = new NetworkCredential(proxyUserName, proxyPassword) }; IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.Proxy = myProxySettings; }); ``` ## HTTP Timeout[​](#http-timeout "Direct link to HTTP Timeout") You can set the maximum wait time for a ConfigCat HTTP response. ```csharp IConfigCatClient client = ConfigCatClient.Get("#YOUR-SDK-KEY#", options => { options.HttpTimeout = TimeSpan.FromSeconds(10); }); ``` The default timeout is 30 seconds. ## Platform compatibility[​](#platform-compatibility "Direct link to Platform compatibility") The *ConfigCat SDK* supports all the widespread .NET JIT runtimes, everything that implements [.NET Standard 2.0](https://learn.microsoft.com/en-us/dotnet/standard/net-standard?tabs=net-standard-2-0)+ and supports TLS 1.2 should work. Starting with v9.3.0, it can also be used in applications that employ [trimmed self-contained](https://learn.microsoft.com/en-us/dotnet/core/deploying/trimming/trim-self-contained) or various [ahead-of-time (AOT) compilation](https://en.wikipedia.org/wiki/Ahead-of-time_compilation) deployment models. Based on our tests, the SDK is compatible with the following runtimes/deployment models: * .NET Framework 4.5+ (including Ngen) * .NET Core 3.1, .NET 5+ (including Crossgen2/ReadyToRun and Native AOT) * Mono 5.10+ * .NET for Android (formerly known as Xamarin.Android) * .NET for iOS (formerly known as Xamarin.iOS) * Unity 2021.3+ (Mono JIT) * Unity 2021.3+ (IL2CPP)\* * Universal Windows Platform 10.0.16299.0+ (.NET Native)\*\* * WebAssembly (Mono AOT/Emscripten, also known as wasm-tools) \*Unity WebGL also works but needs a bit of extra effort: you will need to enable WebGL compatibility by calling the `ConfigCatClient.PlatformCompatibilityOptions.EnableUnityWebGLCompatibility` method. For more details, see [Sample Scripts](https://github.com/configcat/.net-sdk/tree/master/samples/UnityWebGL).
\*\*To make the SDK work in Release builds on UWP, you will need to add `` to your application's [.rd.xml](https://learn.microsoft.com/en-us/windows/uwp/dotnet-native/runtime-directives-rd-xml-configuration-file-reference) file. See also [this discussion](https://github.com/dotnet/runtime/issues/29912#issuecomment-638471351). info We strive to provide an extensive support for the various .NET runtimes and versions. If you still encounter an issue with the SDK on some platform, please open a [GitHub issue](https://github.com/configcat/.net-sdk/issues/new/choose) or [contact support](https://configcat.com/support). ## Troubleshooting[​](#troubleshooting "Direct link to Troubleshooting") When the *ConfigCat SDK* does not work as expected in your application, please check for the following potential problems: * **Symptom:** Instead of the actual value, the default one is constantly returned by `GetValueAsync()` and the log contains the following message (provided that the client is set up to log error level events as described [here](#logging)): "Secure connection could not be established. Please make sure that your application is enabled to use TLS 1.2+." **Problem:** ConfigCat CDN servers require TLS 1.2 or newer security protocol for communication. As for allowed security protocols, please keep in mind that newer .NET runtimes rely on operating system settings, older versions, however, may need additional setup to make secure communication with the CDN servers work. | Runtime Version | Default Protocols | | -------------------------------------------- | ---------------------- | | .NET Framework 4.5 and earlier | SSL 3.0, TLS 1.0 | | .NET Framework 4.6 | TLS 1.0, 1.1, 1.2, 1.3 | | .NET Framework 4.7+, .NET Core 1.0+, .NET 5+ | System (OS) Defaults | As shown in the table above, if your application runs on .NET Framework 4.5, by default it will fail to establish a connection to the CDN servers. Read [this](https://stackoverflow.com/a/58195987/8656352) for more details. **Solution**: The best solution to the problem is to upgrade your application to target a newer runtime but in case that is not possible, you can use the following workaround: ```csharp ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls12; ``` (Place this code at the startup of your application, **before** any instances of `ConfigCatClient` is created.) ## Sample Applications[​](#sample-applications "Direct link to Sample Applications") Check out our Sample Applications how they use the *ConfigCat SDK*: * [Sample Console App](https://github.com/configcat/.net-sdk/tree/master/samples/ConsoleApp) * [Sample Multi-page Web App (ASP.NET Core MVC)](https://github.com/configcat/.net-sdk/tree/master/samples/ASP.NETCore) * [Sample Single-page Web App (ASP.NET Core Blazor WebAssembly)](https://github.com/configcat/.net-sdk/tree/master/samples/BlazorWasm) * [Sample Mobile/Windows Store App (.NET MAUI)](https://github.com/configcat/.net-sdk/tree/master/samples/MAUI) ## Guides[​](#guides "Direct link to Guides") See the following guides on how to use ConfigCat's .NET SDK: * [.NET 6](https://configcat.com/blog/2022/11/25/feature-flags-in-net6/) * [ASP.NET Core](https://configcat.com/blog/2021/10/10/aspnetcore-options-pattern/) ## Look under the hood[​](#look-under-the-hood "Direct link to Look under the hood") * [ConfigCat .NET SDK on GitHub](https://github.com/configcat/.net-sdk) * [ConfigCat .NET SDK on nuget.org](https://www.nuget.org/packages/ConfigCat.Client)